Big Ben’s bong: the science behind its sound

Engineers from the University of Leicester have discovered why London’s iconic Big Ben produces such a distinct bong

Big Ben

The Elizabeth Tower, also known as Big Ben. Credit: Carl Vivian, University of Leicester

It’s the centrepiece of the London skyline, the Elizabeth Tower, fondly known as Big Ben, which has been keeping Londoners on time with its distinct hourly bong for over 150 years.

Now, for the first time ever, a University of Leicester team has been given special access to measure the vibrations of the famous bells for a new BBC Four documentary, Sound Waves: The Symphony of Physics.

Inside Big Ben

Measuring Big Ben’s bong. Credit: BBC

Using ‘laser Doppler vibromety’, a 3D computer model and lasers to map the vibrations as the bells chimed at 9, 10, 11 and 12 o’clock, the team were able to characterise the distinct sound and map the vibrations in the metal of Big Ben that are too tiny to be seen by the naked eye. And the results? As it is thicker and weighs more than other bells of a similar size, the result is a higher pitch than would normally be expected for its diameter. And although when we hear the bell toll we perceive it to be a single sound it is actually made up of a series of distinct frequencies – layered pulsations happening at the same time.

The research has come at an interesting time as Big Ben is about to fall silent for the first time in 30 years as major restoration work takes place. The restoration programme, which will repair the clock, masonry on the tower and rusting metalwork, means Big Ben will remain silent for at least seven months of the three-year project with exceptions made for special events.

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Written by Heidi Finnane // 3rd March 2017

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